diff --git a/src/repr/coords.rs b/src/repr/coords.rs
index f622aeb..11b9f97 100644
--- a/src/repr/coords.rs
+++ b/src/repr/coords.rs
@@ -7,6 +7,7 @@ use static_assertions::const_assert;
 // performance by about 1-2% overall
 pub type CoordAxis = u8;
 
+// using u8 for this results in a ~3-6% perf increase
 pub type CoordPairInner = u8;
 
 const_assert!(CoordPairInner::MAX as usize >= Board::BOARD_AREA as usize);